The present invention relates to methods and apparatuses for automated manufacture of reclosable plastic packages having a resealable closure, especially as part of a form, fill and seal process.
In the use of plastic bags and packages, particularly for foodstuffs, it is important that the bag be hermetically sealed until the purchaser acquires the product, takes it home, and opens the bag or package for the first time. It is then commercially attractive and useful for the consumer that the bag or package be reclosable so that its contents may be protected. Flexible plastic zippers have proven to be excellent for reclosable bags, because they may be manufactured with high-speed equipment and are reliable for repeated reuse.
A typical zipper comprises one fastener strip or closure member having a groove and attached to one side of the bag mouth, and another fastener strip or closure member having a rib and attached to the other side of the bag mouth, which rib may interlock into the groove when the sides of the mouth of the bag are pressed together. Alternatively, a fastener strip having a plurality of ribs may be on one side of the bag mouth, while a fastener strip having a plurality of grooves or channels may be on the other side, the ribs locking into the channels when the sides of the mouth of the bag are pressed together. In the latter case, there may be no difference in appearance between the two fastener strips, as the ribs may simply be the intervals between channels on a strip that lock into another of the same kind. In general, some form of male/female interengagement is used to seal the two sides of the bag mouth together. The fastener strips or closure members are bonded in some manner to the material from which the bags themselves are manufactured.
In the automated manufacture of plastic reclosable packages or bags, it is known to feed a zipper assembly to a position adjacent a sheet of thermoplastic film and then attach the zipper assembly to the bag by means of heat sealing. The zipper assemblies are attached at spaced intervals along the thermoplastic sheet, one zipper assembly being attached to each section of film respectively corresponding to an individual package or bag. The zipper assembly consists of two interlocking fastener strips that typically lie inside the mouth of the package. Each fastener strip preferably has a zipper flange that extends toward the product side of the package in a direction transverse to the line of the zipper. In accordance with one known method of feeding zipper assemblies to an automated form, fill and seal machine, the zipper assembly is in the form of a tape that is unwound from a spool for automated feeding. The tape comprises a continuous length of interlocked fastener strips. The continuous tape is fed to a cutting device that cuts the tape at regular lengths to form an individual zipper. Each individual zipper is then attached to the thermoplastic bag making film by heat sealing or other suitable means. Then the package is formed, filled and sealed on a form-fill-seal (FFS) machine.
Other types of reclosable plastic bags, however, contain a slider that facilitates a consumer opening and re-closing the package by disengaging and re-engaging the two sides of the zipper together. Slide-zipper assemblies are well known in the reclosable packaging art. Conventional slider-operated zipper assemblies typically comprise a plastic zipper having two interlocking profiles and a slider for opening and closing the zipper. In one type of slider-operated zipper assembly, the slider straddles the zipper and has a separating finger at one end that is inserted between the profiles to force them apart as the slider is moved along the zipper in an opening direction. The other end of the slider is sufficiently narrow to force the profiles into engagement and close the zipper when the slider is moved along the zipper in a closing direction. Other types of slider-operated zipper assemblies avoid the use of a separating finger. For example, U.S. Pat. No. 6,047,450 discloses a zipper comprising a pair of mutually interlockable profiled structures and having an A-shaped profile. Portions of the two profiled structures form a fulcrum about which the profiled structures may be pivoted when the slider forces lower edges of the bases towards each other. Above the fulcrum point, the interlocked male and female profiles disengage, thereby opening the zipper. The path of the slider as blocked at opposing sealed ends of the zipper halves by slider end stops, which are typically formed by ultrasonically stomping.
Whether or not the zipper assembly is opened and closed by a slider, the zipper flanges of the zipper assembly, when sealed to the bag making film, must not be sealed to each other. Such “seal-through” of the zipper flanges makes the bag difficult to open and susceptible to losing its reclosability, for example, if the bag film were to be tom during pulling apart of the sealed flanges.
Some techniques for avoiding “seal-through” of the zipper flanges include: inserting an insulating separator plate between the zipper flanges prior to heat sealing the flanges to the bag making film; and constructing the zipper flanges to have confronting layers of high-melting-point thermoplastic material that does not soften during sealing. The use of separator plates is suited more to instances where the zipper assembly is applied to the bag making film in the machine direction, since transverse application would require that the separator plate be repeatedly inserted between the zipper flanges and then retracted. The manufacture of zipper assemblies in which each flange comprises a layer of high-melting-point thermoplastic material laminated to a layer of low-melting-point thermoplastic sealant material is more costly than the manufacture of zipper assemblies without laminated flanges.
U.S. Pat. No. 6,327,837 discloses a zipper assembly having one flange longer than the other. In this case the zipper assembly is initially attached to the bag making film by sealing the portion of the long flange that extends beyond the short flange to the bag making film.
There is a need for an alternative method for automated application of zipper assemblies to bag making film without flange “seal-through”.